The present invention concerns packages for an integrated circuit device, substrates for making such packages, and methods of making the packages and substrates.
U.S. Pat. No. 5,859,475 to Freyman et al. describes several ball grid array style packages for an integrated circuit device. The packages include a thin planar polyimide sheet. In one embodiment, a die pad and metal traces are formed on the upper surface of the polyimide sheet. An integrated circuit device is mounted on the die pad and is connected by bond wires to the metal traces. Metallized vias extend through the polyimide sheet and connect the metal traces on the upper surface of the sheet to metal traces on the opposite lower surface of the sheet. Solder balls are connected to the metal traces on the lower surface of the polyimide sheet. In another embodiment, a die pad and metal traces are formed on the upper surface of the polyimide sheet. The metal traces terminate in a metal land. Solder balls are directly attached to the backside of the metal land through apertures in the polyimide sheet. In both of these embodiments, bond wires, solder balls, metal traces, and metal-filled vias are used. Each of these features contribute to the cost of a package, and thus elimination of any of them will reduce costs. In addition, the packages do not include a means for enhanced thermal performance.
The present invention improves on the prior art by providing integrated circuit device packages that are thinner than conventional packages and have improved thermal performance. The packages and the substrates and methods of making them also are reliable, and cost effective in that the substrates and packages are assembled using conventional materials and equipment.
One embodiment of a substrate within the present invention includes a planar nonconductive sheet having a first surface, an opposite second surface, and first apertures between the first surface and second surface. The nonconductive sheet may be polyimide, plastic, or an epoxy laminate. The substrate also includes a planar metal die pad and planar metal leads. The die pad and leads each have a first surface and an opposite second surface. The first surfaces of the die pad and leads are attached to the nonconductive sheet. Each first aperture in the nonconductive sheet is juxtaposed with the first surface of a lead.
Packages made using the inventive substrates also are within the present invention. One embodiment of a package within the present invention includes an integrated circuit device that is mounted above the first surface of the die pad. Bond wires are conductively connected between the integrated circuit device and the first surface of the leads through the first apertures in the nonconductive sheet. An encapsulating material on the first surface of the nonconductive sheet covers the integrated circuit device, the bond wires, and the first apertures. The second surfaces of the die pad, leads, and nonconductive sheet are exposed at a lower exterior surface of the package.
These and other embodiments of the invention are described in greater detail below.